The invention relates to novel Polyalkylene glycol bisphenyl-A-sulfopropyl diethem and salts thereof. Also disclosed is a process for their use as additives to electroplating baths, particularly acid zinc electroplating baths, for the purpose of enhancing the appearance, integrity, and performance of the electroplated deposits.
U.S. Pat. No. 4,820,388 (Kurze), incorporated herein in its entirety by reference, reveals novel compositions of matter comprising polyalkylene glycol naphthyl-3-sulfopropyl diethers and their use as surfactants in electroplating baths. These compounds and the process revealed, have worked well, however, these compounds have a significant drawback, a relatively low cloud point in aqueous solutions when reasonable concentrations of the compounds are utilized, i.e. from 1 to 2 g/L of the compound. Higher cloud points are only obtainable with these compounds in aqueous solution when very high concentrations are utilized (from 3 to 10 g/L).
The cloud point of a compound is the temperature at which the compound begins to precipitate out of solution at a given concentration and solvent mixture. Thus, it has been discovered that the compounds of Kurze possess a relatively low cloud point, particularly under the conditions that they are used in electroplating baths as performance additives.
Electroplating baths, by their very nature, tend to rise in temperature during use because of the current necessary for operation and the solution's electrical resistance. Therefore, as an electroplating bath is used and it heats up, compounds such as the Kurze compounds which have low cloud points at the concentrations effectively utilized in electroplating solutions, will begin to precipitate from solution. This precipitation of these compounds and the other additives which they solubilize, then causes poor bath performance and inconsistency in the plating results. Thus, the performance of electroplating baths can be measurably improved by utilizing plating additives with higher cloud points.
It has now been found that the compounds of the present invention provide all of the advantages of the prior art compounds along with an additional advantage of processing a higher cloud point at any given concentration in aqueous solution, particularly when utilized as electroplating bath performance additives.